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    <title>Reinterpreting Types Using as_typen()</title>
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      <div xmlns="" class="refnamediv">
        <a xmlns="http://www.w3.org/1999/xhtml" id="Reinterpreting Types Using as_typen()"></a>
        <h1>Reinterpreting Types Using as_typen()</h1>
        <p>
            Reinterpreting Types Using as_type<code xmlns="http://www.w3.org/1999/xhtml" class="varname">n</code>()
        </p>
      </div>
      <div class="refsect2">
        <a id="synopsis"></a>
        <h3></h3>
        <div class="informaltable">
          <table class="informaltable" border="0">
            <colgroup>
              <col align="left" class="col1" />
            </colgroup>
            <tbody>
              <tr>
                <td align="left">
as_typen()
                        </td>
              </tr>
            </tbody>
          </table>
        </div>
      </div>
      <div class="refsect1">
        <a id="description"></a>
        <h2>Description</h2>
        <p>
All data types described in
<a class="citerefentry" href="scalarDataTypes.html"><span class="citerefentry"><span class="refentrytitle">Scalar Data Types</span></span></a> and
<a class="citerefentry" href="vectorDataTypes.html"><span class="citerefentry"><span class="refentrytitle">Vector Data Types</span></span></a>) (except <span class="type">bool</span>, <span class="type">half</span>, and <span class="type">void</span>) may be also reinterpreted as another data type of the same size using the <code class="function">as_type<em class="replaceable"><code>n</code></em>()</code> operator. When the operand and result type contain the same number of elements, the bits in the operand shall be returned directly without modification as the new type. The usual type promotion for function arguments shall not be performed.
        </p>
        <p>
For example, <code class="code">as_float(0x3f800000)</code> returns <code class="code">1.0f</code>, which is the value that the bit pattern <code class="code">0x3f800000</code> has if viewed as an IEEE-754 single precision value.
        </p>
        <p>
When the operand and result type contain a different number of elements, the result shall be implementation-defined. That is, a conforming implementation shall explicitly define a behavior, but two conforming implementations need not have the same behavior when the number of elements in the result and operand types does not match. The implementation may define the result to contain all, some or none of the original bits in whatever order it chooses. It is an error to use <code class="function">as_type<em class="replaceable"><code>n</code></em>()</code>
operator to reinterpret data to a type of a different number of bytes.
        </p>
      </div>
      <div class="refsect1">
        <a id="notes"></a>
        <h2>Notes</h2>
        <p>
While the union is intended to reflect the organization of data in memory, the
<code class="function">as_type<em class="replaceable"><code>n</code></em>()</code> construct is intended to
reflect the organization of data in register. The
<code class="function">as_type<em class="replaceable"><code>n</code></em>()</code> construct
is intended to compile to no instructions on
devices that use a shared register file designed to
operate on both the operand and result types. 
        </p>
        <p>
Note that while differences in memory organization are expected
to largely be limited to those arising from endianness,
the register based representation may also differ due to
size of the element in register. (For example, an
architecture may load a char into a 32-bit register, or a
char vector into a SIMD vector register with fixed 32-bit
element size.) 
        </p>
        <p>
If the element count does not match, then
the implementation should pick a data representation that
most closely matches what would happen if an appropriate
result type operator was applied to a register containing
data of the source type. If the number of elements matches, then the
<code class="function">as_type<em class="replaceable"><code>n</code></em>()</code>
should faithfully reproduce the behavior expected from a
similar data type reinterpretation using memory/unions.
So, for example if an implementation stores all single
precision data as double in register, it should implement
as_int( float )
by first downconverting the double to single
precision and then (if necessary) moving the single
precision bits to a register suitable for operating on
integer data.
        </p>
        <p>
  If data stored in different address spaces do not have the same endianness, then the "dominant endianness" of the device should prevail.
        </p>
      </div>
      <div class="refsect2">
        <a id="example1"></a>
        <h3>
            Example
        </h3>
        <div class="informaltable">
          <table class="informaltable" border="0">
            <colgroup>
              <col align="left" class="col1" />
            </colgroup>
            <tbody>
              <tr>
                <td align="left">
float f = 1.0f;
uint u = as_uint(f);  // Legal. Contains:  0x3f800000

float4 f = (float4)(1.0f, 2.0f, 3.0f, 4.0f);
// Legal. Contains: (int4)
// (0x3f800000, 0x40000000, 0x40400000, 0x40800000)
int4 i = as_int4(f);

float4 f, g;
int4 is_less = f &lt; g;

// Legal. f[i] = f[i] &lt; g[i] ? f[i] : 0.0f
f = as_float4(as_int4(f) &amp; is_less);

int i;
// Legal. Result is implementation-defined.
short2 j = as_short2(i);

int4 i;
// Legal. Result is implementation-defined.
short8 j = as_short8(i);

float4 f;
//Error. result and operand have different size
double4 g = as_double4(f);
                        </td>
              </tr>
            </tbody>
          </table>
        </div>
      </div>
      <div class="refsect1">
        <a id="specification"></a>
        <h2>Specification</h2>
        <p>
            <img src="pdficon_small1.gif" />
                                                 
            <a href="http://www.khronos.org/registry/cl/specs/opencl-1.0.pdf#page=141" target="OpenCL Spec">OpenCL Specification</a>
        </p>
      </div>
      <div class="refsect1">
        <a id="seealso"></a>
        <h2>Also see</h2>
        <p>
            <a class="citerefentry" href="scalarDataTypes.html"><span class="citerefentry"><span class="refentrytitle">Scalar Data Types</span></span></a>, 
			<a class="citerefentry" href="vectorDataTypes.html"><span class="citerefentry"><span class="refentrytitle">Vector Data Types</span></span></a>
        </p>
      </div>
      <div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2009 The Khronos Group Inc. 
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and/or associated documentation files (the
"Materials"), to deal in the Materials without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Materials, and to
permit persons to whom the Materials are furnished to do so, subject to
the condition that this copyright notice and permission notice shall be included
in all copies or substantial portions of the Materials. 
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